Pivoted fence with locating post

ABSTRACT

A router and other cutting tools with a fixed center such as drills, shapers, milling machines, etc., used for cutting wood, metal or other materials, is provided with a fence mechanism for either a table or the base of a portable tool, for rapid and easy settings of the fence with respect to the center of the cutting tool. This is accomplished by a pivot mounting of the fence on a table or on a portable tool base, with respect to a block pivoted to the table or tool base, wherein the center of the pivot for the block and the center for the pivot for the fence are on opposite sides of the cutting tool and located on a line which passes through the tool center and the respective pivot locations. The desired spacing of the fence to the tool can be achieved using accurate spacers between the fence and the block, even with the tool being mounted in place. When used on a table, a curved slot in the table top, of predetermined shape and location with respect to the tool center, can be provided to receive a follower pin extending from the fence and function to move the fence in fence centered motion. The disclosure teaches how to develop such a curved guiding slot.

BACKGROUND OF THE INVENTION

The concept of using two pins or posts mounted on a router base to makea self-centering mortising and slotting base is per se well known.Spielman in his book "Router Jigs & Techniques" (1988 SterlingPublishing Co., Inc. New York N.Y.) describes such a base on page 202. Amore recent application of the concept is described by Taylor andMcDaniel in U.S. Pat. No. 5,423,360 where an apparatus for centering awork-piece relative to a cutting tool is disclosed. That concept couldbe adapted directly to a router table T, with a router (not shown)mounted to a base plate 14 (or a table for other tools such as drills,shapers etc.) as illustrated in FIG. 1 herein (Prior Art).

Thus, two posts 13a and 13b could be fixed to a table with pivots 12aand 12b, the posts being centered on each side of the cutting tool on aline through the center of the cutting tool 15. The posts could be, forexample, four inch diameter disks cut from three-quarter inch stock.Although the arrangement illustrated in FIG. 1 could work for centeringa work-piece it would be difficult to use and not truly practical.However, with certain unique modifications described hereinafter, such adevice can be very useful not only for centering the workpiece but alsoin setting up the fence of a router table to perform various cuts.

SUMMARY OF THE INVENTION

Even though a router table is used as an example, it is clear that theconcept can be used with various other cutting tools with a fixed centersuch as drills, shapers, milling machines, etc., whether used forcutting wood, metal or other materials. The most important uniquefeature of this invention is the provision of a fence mechanism, foreither a table or a portable tool, which provides rapid, easy to use,settings of the fence with respect to the center of a cutting tool, suchas a router bit. This is accomplished by a pivot mounting of the fenceon a table or on a portable tool base, with respect to a block pivotedto the table or tool base, wherein the center of the pivot for the blockand the center for the pivot for the fence are on opposite sides of thecutting tool and located on a line which passes through the tool centerand the respective pivot locations. The desired spacing of the fence tothe tool can be achieved using accurate spacers between the fence andthe block, even with the tool being mounted in place.

When the invention is installed on a table, a curved slot ofpredetermined shape and location with respect to the tool center willreceive a follower pin extending from the fence, and provides a meansfor positioning the fence to provide fence centered motion such thatwhen the fence is moved over the table the center of the fence willalways align with the center of the cutting tool (i.e. the center of thefence and the center of the cutting tool lie on a line perpendicular tothe fence.) The disclosure teaches how to develop such a curved guidingslot.

Also disclosed are various jigs and relationships which can be used tolocate desired centers of pivot locations on the table, or on a toolbaseplate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) shows two posts pivotally attached to a table andequally spaced from a cutting tool on a line extending through the toolcenter;

FIG. 2 shows the post arrangement of FIG. 1 together with a fencepivotally attached to the table;

FIG. 3 illustrates the use of a spacer of known dimension to space thefence a desired distance from the cutting toll;

FIG. 4 is a view, from the back of table T, similar to FIG. 3 withexemplary dimensional relationships;

FIG. 5 illustrates the pivoted fence and post on a table as used todevelop an equation for the cutting of a groove in the table (or fence)to receive a follower pin in the fence (or table), such that when thefence is moved over the table the center of the fence will always alignwith the center of the cutting tool.

FIG. 6 is a diagram illustrating the development of curves which definethe shape of a slot, as in the fence base, to receive a follower in thetable top and achieve fence centered motion of the fence with respect tothe cutting tool;

FIG. 7 is a diagrammatic expression of the shape of such a slot cut inthe table top, to receive a follower in the fence and achieve fencecentered motion of the fence with respect to the cutting tool;

FIG. 8 is an illustration of a jig for cutting (routing) a fencecentered motion curve into the table;

FIG. 9 is an illustration of a jig for pivot hole layout on the table;

FIG. 10 is an illustration of a router baseplate fitted with a pivotedfence and locating post;

FIG. 11 illustrates use of the pivoted fence and locating post as adrilling and marking jig.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 2, the router fence can be attached to theleft-hand post 13a so its face is tangent to the post as shown. The lefthand post 13a does not need to be present; all that is required is thatthe fence 16 be attached to the table by a pivot 12 located at thecenter of the original post 13a. The pivot hole in the fence 16 islocated relative to the face 17 of the fence at a distance equal to theradius of the post 13b, e.g. 2 inches for the 4 inch diameter post inthe example. With this arrangement, the left-hand post is replaced bythe fence 16 and pivot 12a. In a similarly way, the right hand circularlocating post 13b in FIG. 2 could be replaced with a rectangularlocating post, provided that the edge facing the fence is tangent to theoriginal circular locating post 13b.

If a board (i.e. work-piece) is placed against the fence face 17 andboth are rotated until the work-piece contacts the locating post, thenthe board is perfectly centered relative to the cutting tool regardlessof the thickness or width of the board. The fence 16 can then be clampedto the table T, the locating post 13b removed and, if desired, stopblocks positioned on the fence 16. The fence 16 can then be used to makethe desired, centered cuts in as many pieces of the same size asrequired.

In order to ensure accuracy over time, means can be provided to adjustthe position of one of the pivots 12a and 12b. Using a simple jig, thetable could be realigned, e.g. after a new router is installed in thetable.

The automatic centering feature in itself would make the pivoted fencewith locating post worth while, however, it is also very simple toaccurately set up other jobs, that do not require centering.

The pivoted fence with locating post is exactly the same as any otherpivoted fence when the locating post 13b is removed. In mostapplications, the fence face 17 is located behind the center of thecutting tool 15, but for some applications the fence face 17 is in frontof the center of the cutting tool 15. However, when the fence 17 isbehind the cutting tool, the pivoted fence with locating post is easy toset up for various cuts and will be discussed first.

The pivoted fence with locating post can be used to accurately set thefence face 17 a required distance from the center of the cutting toolvery easily. As shown on FIG. 3, all that is required is a spacer 18 oftwice the desired setting: e.g. if you want the center of the cuttingtool 15 to be 3/16 inch from the edge of the work piece, then use a 3/8inch spacer 18 between the fence face 17 and the locating post 13b. Mostwell equipped shops have very accurate spacers available in drill bits,and can be used, as shown in FIG. 3, to accurately set up the fence. Ifno spacer 18 of the right size is available, then measurements can bemade with a square or other suitable means.

One edge of the square must be against the fence face 17 and the otheralong a diameter of the locating post pivot 12b. The measurement, ofcourse, is twice the required spacing at the bit center B from the fenceface 17. If the rectangular locating post is used, the edge facing thefence face must be parallel to the fence when the measurement is made;this is easily accomplished with a square. However, a better option isto attach or build into the locating post a means for making accuratemeasurements, for example a vernier caliper or an Incra gauge.

If the fence face 17 is rotated against the left locating post 13b (i.e.no spacer), then the face of the fence is exactly over the center of thecutting tool 15. If it is desired to set the fence face 17 ahead of thecutting tool, a slightly more complicated approach is required asdescribed hereinafter.

If it is desired to set the fence face 17 to a known distance ahead ofthe cutting tool center 15 or to reference the set up distance to thefront of the cutting tool, smaller locating posts of known radius can beused to set up the fence 16. The distance that the fence face 17 isadvanced ahead of the cutting tool center is one-half of the differencebetween the smaller radius and the original locating post radius. Thus,if the original locating post has a radius of two inches, and the newlocating post has a radius of one & one-half inches, then the face ofthe fence face 17 is one quarter inch ahead of the cutting tool center15 (i.e. 1/4=(2-1.5)/2) which would also allow set up distances to befrom the front edge of a 1/2 inch bit. Again, it is also possible to usea square and measure to the required small radius.

If a rectangular locating post is used, the pivot can be located so thatthe first edge is set to the same distance from its pivot as the fenceface 17 is located from the fence pivot 12a, while each of the otherthree edges is set closer to the pivot at different distances. Hence,each edge can be used to set the fence face 17 ahead of the cutting toolcenter 15 by different amounts. Each edge can be set to measure the setup distance from the edge of different size cutting tools.

For completeness, the next section shows how the pivoted fence andlocating post works and gives the information needed to make a fencewith a ratio different than 1/2.

Function of the Pivoted Fence & Locating Post

FIG. 4 shows a general scheme for setting up a pivoted fence andlocating post. In general the centers of the locating post 13b, pivot13a and cutting tool 15 must all lie on the same line but the spacing 51and 52, need not be the same. That is, S₁ and S₂ do not need to beequal. The distance from the face of the fence to the pivot is r₁ and,in general, it does not need to be equal to the radius of the locatingpost r2.

Even with these generalizations, the similar triangles, shown bold inFIG. 4, can be used to describe how the pivoted fence and locating postworks. The triangle "acd" is similar to the triangle "abe" and all ofthe similar sides are in the ratio of S₁ /(S₁ +S₂) which is called R;note that if S₁ =S₂ then the ratio, R, is 1/2 as it was in the previousdiscussion.

The sides "eb" and "cd" are similar sides and, therefore are in theratio R. The side "eb" is the sum of r₁ and the set-up distance (theperpendicular distance from the fence face 17 to the cutting tool center15). The side "cd" is the sum of r₁, the spacer 18 (or measured)distance and r₂. Consequently:

    (setup+r.sub.1)/(r.sub.1 +spacer+r.sub.2)=S.sub.1 /(S.sub.1 +S.sub.2)

The relation obtained above from the similar triangles can be used todetermine how the setup distance is related to the spacer 18 and thephysical dimensions illustrated in FIG. 4. The resulting relationship is

    setup= S.sub.1 /(S.sub.1 +S.sub.2)!(r.sub.1) r.sub.2 /r.sub.1 -S.sub.2 /S.sub.1 !+ S.sub.1 /(S.sub.1 +S.sub.2)! (spacer)

It should be noted that if the physical dimensions of the locating post13b and fence pivot 13a are chosen wisely, the term involving only thephysical dimensions will not be needed: i. e. chose

    r.sub.2 /r.sub.1 =S.sub.2 /S.sub.1

Using the above relation for the physical dimensions results in a simplerelationship for the setup distance:

    setup= S.sub.1 /(S.sub.1 +S.sub.2)! (spacer)

For example, if the pivot 13a is located one inch from the face of thefence 17, then, r₁ is 1 inch. If the locating post 13b and pivot 13a arecentered at 15 inches on each side of the cutting tool center 15, on aline through the center 15 of the cutting tool, using a 1 inch radiuslocating post 13b, obtains a ratio of 1/2. Then, using the same fence 16and table T, by adding two additional holes (not shown) for the fencepivot 13a, along the line through the center of the cutting tool, all ofthe ratios shown in Table 1 can be obtained.

                  TABLE 1    ______________________________________    Required Dimensions to Obtain Various Ratios    with the same Fence and Table    Dimension/ratio                  1/2        1/3       1/4    ______________________________________    Pivot Radius r.sub.1                  1 inch     1 inch    1 inch    Post Radius r.sub.2                  1 inch     2 inch    3 inch    Pivot Space S.sub.1                  15 inch    71/2 in.  5 inch    Post Space S.sub.2                  15 inch    15 inch   15 inch    ______________________________________

It is interesting to note that one can mortise or groove a board at itscenter or at one fourth of its thickness (or width), or at one third ofits thickness (or width). Using a 1" spacer, with a ratio of 1/3, wouldeven let us cut a groove 1/3 inch from the edge.

Thus the pivoted fence with a locating post affords a simple andaccurate method for centering work and setting up the fence for othercuts. However, the pivoted fence has a drawback when one wants to cut ablind rectangular mortise wider than the bit: when the fence is moved,any stop blocks being used would have to be adjusted to obtain thedesired result. Also, if a work piece is held firmly against the fenceand the fence is moved then the bit will cut an arc in the piece ratherthan a cut perpendicular to the edge that was held against the fence. Asdescribed in the next section, we have solved these problems with theconcept of "fence centered motion".

Fence Centered Motion

The term fence centered motion, means that when the fence is moved, thefence is located so that the center of the fence lies on a line that isperpendicular to the fence and passes through the center of the bit.This can be accomplished by cutting a slot in the fence that replacesthe fence pivot hole and by cutting a groove in the table that guides afollower (e.g. a peg) in the fence. Alternately, the peg can be attachedto the table T and both a straight slot and a curved slot can be cutinto the fence. The equations for the curve and the location of the pegare developed as follows.

FIG. 5 shows the table with the fence, 16, pivoted at some arbitraryangle, θ. Both the fence and the table coordinates are shown on FIG. 5.FIG. 5 also shows the angles and distances referred to in thedescriptions of the equations in the following sections.

X and Y are the coordinates of a point on the fence which will trace acurve in table coordinates. Sp (see FIG. 5) is the perpendicular spacingof the fence face, 17, from the center of the router bit, 15, which isthe origin of the table coordinates. When the spacing, Sp, is zero theorigin of the fence and the table coincide. Lower case r is the locationof the center of the fence pivot, 12a, from the face of the fence, 17,(likewise, r is the radius for the post 13b.) Lower case s is thespacing of the pivot holes, 12a and 12b, from the center of the routerbit, 15, (11.09375 in the prototype table). The angle θ₀ is between thefence face 17, and the diameter through the pivot holes, 12a and 12b,when the spacing, Sp., is zero.

    Sp(θ)=s sin (θ(π/180)-r!

The angle θ above is between the fence face 17 and the diameter throughpivot holes 2, at the fence position that gives the spacing Sp.

    α(θ)=π/180(θ)-θo(r)

The angle α, above, is between the face of the fence, 17, and the x axisof the table (the line tangent to both posts 13a and 13b).

    X(x,θ)=y sin (α(θ))+x cos (α(θ))

    Y(x,θ)=y cos (α(θ))-x sin (α(θ))-Sp (θ)

The above two equations give the trace of the point x, y that is fixedto the table, on the fence. (the values of X and Y are in fencecoordinates.) as a function of the parameter θ. FIG. 6 shows such curvesfor y=r and example values of x as indicated on FIG. 6: the tracingpoints are located in table coordinates at: (-13, 2), (-12.5, 2), (-12,2) and at the fence pivot point. If a slot is cut into the fence alongthe pivot point trace then the fence can pivot and be moved along theslot to align the center (the origin in fence coordinates) of the fencewith the bit (the center of the bit, 15, and the origin of the fence lieon a line perpendicular to the fence face.) If a groove is, also, cutinto the fence along one of the other traces and a follower located inthe table at the tracing point, then when the fence is mounted to thetable and it is moved the center of the fence will always align with thecenter of the bit.

If X and Y are the fence coordinates of a point fixed on the fence. thenthe trace of the point X,Y (fixed to the fence) on the table (x and yare in table coordinates) is given as:

    x(X,θ)=X cos (α(θ))-(Sp(θ)+Y) sin (α(θ))

    y(X,θ)=X sin (α(θ))+(Sp(θ)+Y) cos (α(θ))

Thus, an alternate approach is to cut the trace into the table as shownin FIG. 7. The follower is then placed in the fence at the proper point(here at (10, 2) as in the prototype table) and again the fence (with astraight slot as above) can be moved and the center automaticallyaligned with the bit.

The equations given above can be used in computer controlled equipmentused in the manufacture of the tables. However, a simple jig has beendeveloped which allows cutting of the required curve into the tableusing a router. FIG. 8 shows a schematic of the jig used to cut thecurve into the prototype table. The two slots are perpendicular and therouter bit is mounted on the jig at the same relative position as thefollower pin will be at, on the fence. The pivot pin of the fence isplaced through the slot, 27, and into the pivot hole in the table andthe router bit of the router mounted in the table (not used to cut thecurve) is inserted into the slot, 28, in FIG. 5. When the router ismounted on the jig and is moved while running, it cuts the requiredcurve for fence centered motion into the table.

Also, a simple jig was developed for layout of the pivot holes, as shownin FIG. 9. As an example, a 1/4 inch hole, 23, in the jig is positionedover a 1/4 inch rod or bit mounted in the router. The jig is rotated tothe desired position and clamped to the table. Using the bottom edge ofthe slots,24, two lines are drawn. These lines, if extended, would passthrough the center of the cutting tool. The clamp is removed and the jigis allowed to rotate about the bit center. One of the holes, 26,provided in the jig is then used to swing an arc across each of the linesegments: the intersection of the arcs with the lines precisely locatethe centers of the pivot hole for the fence and the locating post.

The simple jigs, shown in FIGS. 8 and 9, can be provided in kits, alongwith instructions, that would allow a user to make, or upgrade, a tablein the user's own workshop. In addition to the fixed table applications,so far discussed, there are numerous applications of the concept forportable tools such as drills and routers (not table mounted). Some ofthese are discussed in the next section.

Portable Power Tool Applications

A router baseplate can be equipped with a pivoted fence with locatingpost for use in portable applications, as shown in FIG. 10. Thus, thecentering feature and ease of setup afforded by the pivoted fence withlocating post will be available for portable applications. The locatingpost can be equipped with measurement means for those applications thatdo not require centering, just as in the table mounted case.

It should be pointed out that the pivoted fence with locating postavoids the limitations of both work piece size and mortise location thata traditional baseplate with two pins, centered about the bit,experiences: the work piece must be long enough to permit both pins tocontact opposite sides of the work piece for the entire length of thecut. Further, irrespective of the length, the cuts cannot be made closeto either end of the work piece, since, both pins must stay in contactwith the work piece for the entire length of the cut. Even through itmay be possible to work around these limitations it is not necessarywith the pivoted fence with locating post. Neither of the limitationsapply to the pivoted fence with locating post, since, once set up thework piece rides against the fence and, therefore, can be machined fromone end to the other regardless of the length of the work piece.

The pivoted fence with locating post can also be used with portabledrills. The pivoted fence and locating post can be attached to thebottom of a drill fixture, used for drilling holes vertically or at aset, fixed angle. Both the self centering feature and the locatingfeature can be used for vertical drilling. An alternate approach is touse the pivoted fence with locating post as a self centering jig withmeans for attaching drill bushings or marking tools at the center of thejig, as shown in FIG. 10. After the fence is located at the desireddistance, the fence is locked in place and the post removed. Thus, thebushing or marking tool is located precisely relative to the fence andas many holes as desired can be drilled, or a straight line can bemarked on the work piece. Means (not shown) can be attached to thebushing to allow for evenly spaced holes: e.g. a holder, with a pinequal to the bit diameter, could be pivoted around the bushing and usedto locate the jig for the next hole.

While the methods herein described, and the forms of apparatus forcarrying these methods into effect, constitute preferred embodiments ofthis invention, it is to be understood that the invention is not limitedto these precise methods and forms of apparatus, and that changes may bemade in either without departing from the scope of the invention, whichis defined in the appended claims.

What is claimed is:
 1. A fence mechanism providing rapid and simplifiedsettings of a fence member with respect to the center of a rotarycutting tool, in which the cutting tool is mounted to rotate in linewith a center point in a base member,a base member having a center pointproviding a reference to the rotational axis of the cutting tool, afence member extending at least partially across said base member pastsaid center point a stop member to one side of said aperture forproviding a rest which a first portion of the fence can contact forpositioning, a pivot connection between said fence member and said basemember located on said fence member at the opposite side of saidaperture from said stop member such that said fence member can be swungabout said pivot connection into contact with said stop member with acentral portion of said fence member intersecting the axis of rotationof the cutting tool, whereby movement of said first portion of saidfence member a predetermined distance away from said stop member willcause said central portion of said fence member to locate at apredetermined spacing from the tool axis of rotation so workpieces canbe guided with respect to the rotating tool as the workpiece and toolare moved relative to each other.
 2. A fence mechanism as defined inclaim 1, wherein said base member is a base plate of a portable tool andsaid fence member is attached to said base plate.
 3. A fence mechanismas defined in claim 1, wherein said base member is a table having anupper surface with said center point thereon and to which the rotarycutting tool is aligned, andsaid fence member is mounted to the uppersurface of said table.
 4. A fence mechanism as defined in claim 3,wherein said table upper surface includes a curved slot located withrespect to said stop member and said center point,said fence memberhaving a straight slot therein and said fence member pivot connection isfixed to said table surface and has a sliding connection to saidstraight slot, a curved slot formed in said table surface, and afollower on said fence member which tracks along said curved slot.
 5. Afence mechanism as defined in claim 1, wherein measuring means areassociated with said stop member to provide precise spacing of said stopmember and said first portion of said fence member, thereby to provideprecise spacing between said central portion of said fence member andthe rotary cutter regardless of the presence and/or size of the rotarycutter.
 6. A fence mechanism as defined in claim 1, wherein said stopmember includes a disc for contacting said first portion of said fencemember.
 7. For use with a rotary cutting tool mounted to rotate in anaperture in a base member, a fence mechanism for setting the position ofa fence member with respect to the center of the rotary cutting tool,comprisinga base member having a central aperture providing asurrounding through which the cutting tool can project, a fence memberextending perpendicularly to and at least partially across said basemember past said aperture, a stop member to one side of said aperturefor providing a rest which a first portion of the fence can contact forpositioning, a pivot connection between said fence member and said basemember located on said fence member at the opposite side of saidaperture from said stop member such that said fence member can be swungabout said pivot connection into contact with said stop member with acentral portion of said fence member extending across said aperture andintersecting the axis of rotation of a cutting tool when mounted,whereby movement of said first portion of said fence member apredetermined distance away from said stop member will cause saidcentral portion of said fence member to locate at a predeterminedspacing from the tool axis of rotation so workpieces can be guided withrespect to the rotating tool as the workpiece and tool are movedrelative to each other.
 8. A fence mechanism as defined in claim 7,whereinsaid base member is a base plate of a portable tool and saidfence member is attached to said base plate.
 9. A fence mechanism asdefined in claim 7, whereinsaid table upper surface includes a curvedslot located with respect to said stop member and said aperture, saidfence meber having a straight slot therein and said fence member pivotconnection is fixed to said table surface and has a sliding connectionto said straight slot, a curved slot formed in said table surface, and afollower on said fence member which tracks along said curved slot.
 10. Afence mechanism as defined in claim 9, whereinsaid table upper surfaceincludes a curved slot located with respect to said stop member and saidaperture and said fence member pivot connection is a follower on saidfence member which tracks along said slot.
 11. The method of setting theposition of a fence member with respect to the center of a rotarycutting tool mounted to rotate in an aperture in a base member,comprisingmounting a fence member extending perpendicularly to and atleast partially across the base member and past the aperture, locating astop member to one side of the aperture providing a rest which a firstportion of the fence can contact for positioning, providing a pivotconnection between the fence member and the base member which is locatedon the fence member at the opposite side of the aperture from the stopmember such that the fence member can be swung about the pivotconnection into contact with the stop member, thus locating a centralportion of the fence member extending across the aperture andintersecting the axis of rotation for a cutting tool, moving the firstportion of the fence member a predetermined distance away from the stopmember to cause the central portion of the fence member to locate at apredetermined spacing from the tool axis of rotation so workpieces canbe guided with respect to the rotating tool as the workpiece and toolare moved relative to each other.